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Linear Regulator Fundamentals

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Linear Regulator Fundamentals

2.2 NPN

- Voltage feedback samples the outputR1 and R2 may be internal or external
- Feedback controls pass transistor’s current to the load

V

V

IN

OUT

PASS

TRANSISTOR

R1

ERROR

C

AMP

C

IN

R

OUT

LOAD

R2

V

REF

- The NPN-Quasi-LDO has the following Characteristics:
- Requires the input voltage to be at least 0.9V to 1.5V higher than the output voltage
- Has higher Ground pin current than the NPN-Darlington, but less than the PNP-LDO Voltage Regulators
- Requires an output capacitor, but, generally, has no specific ESR requirement like the PNP-LDO

Simple Model of Losses in the NPN "Quasi-LDO"

The drive current for a load current requirement of 5mA

Increasing the load current requirement to 500mA

- The NPN-Quasi-LDO has the following Characteristics:
- Requires the input voltage to be at least 0.9V to 1.5V higher than the output voltage
- Has higher Ground pin current than the NPN-Darlington, but less than the PNP-LDO Voltage Regulators
- Requires an output capacitor, but, generally, has no specific ESR requirement like the PNP-LDO